System of reversing prisms



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March 3, 1931. Q MLLER I 1,795,092

SYSTEM OF RENEE SING PRISKS Filed June 28, 192a T l5 9 7 UNITED STATESPATENT OFFICE or'ro Mom or WEDEL, GERMANY, ASSIGNOB TO THE FIRM or CARLZEISS, or JENA, GERMANY SYSTEM OF REVERSING PRISMS Application filedJune 28, 1928, Serial No. 288,865, and in Germany June 18, 1926.

The present invention relates to an image reversing system of prismsaffording parallel vision, in which only two ray-traversing surfaces areexposed to the air, and in which there is only one roof surface and twosingle totally reflecting surfaces, thus dispensing with any silvering.

If a prism-system of the said kind is de veloped in such a way as tohave one of the two single reflecting surfaces border one of the tworay-traversing surfaces at a re-entering angle, if further suchprism-system consists 0 two glass bodies cemented to each other, withthe position of the cemented surface being such as to contain thatparticular edge upon which the vertex of the said angle lies, and if thesaid roof surface is so disposed as to be the last reflecting surfacestruck y a ray traversing the prism, an advantage is attained over theaforementioned types of prism-systems, which are well known, in that thedistance from each other of the two raytraversing surfaces may be ke tsmall, this being an important factor, particularly if the prism-systembe applied to field-glasses.

It is convenient to distribute the reflecting surfaces amongst the twoglass bodies in such a manner as to have one glass body contain only theroof, and the remaining glass body only the two single reflectingsurfaces. Therefore, it is preferable that only one of the tworay-traversing surfaces be assigned to each one of the two glass bodies.

A particular advantage is attained if the angle of inclination of theroof towards the ray-traversing surfaces be kept rather small, lyingbetween, say, 8 and 22. In this way it is possible to obtain prism formsin which each of the two glass bodies protrudes beyond theray-traversing surface of the other, in a perpendicular direction to theray-traversing surfaces, thus preventing a direct transview through thetwo ray-traversing surfaces, and the formation, therefore, of disturbingreflections.

In Figs. 1 to 7 of the annexed drawing there are shown in principalsection, seven prism-systems as in accordance with the invention.

The prism-system in Fig. 1 contains two single totally reflectingsurfaces at and b, and a roof 0. The ray-traversing surface d liesparallel to the ray-traversing surface e. The latter surface togetherwith the adjacent reflecting surface 1) forms a re-entering angle a 170, while the angle B, which is embraced by the edge of roof 0 and by theaforesaid two ray-traversing surfaces 03 and e, is 22. By a plane 7,containing the vertex A of the said angle oz, the prism-system isseparated into parts I and II to be cemented together. The position ofthe plane 7 is such, as to make part I of the prism-system contain theroof 0, in addition to the two single reflecting surfaces a and b.

The prism-systems shown in Figs. 2 and 3 merely differ from the oneshown in Fig. 1 by the different position of the plane 7 dividing eachrism-system into two parts.

In ig. 2 the two reflecting surfaces a and b belong to part I and theroof to part II, whereby the plane f, as in Fig. 1, passes through thevertex A of the said angle a, and whereby both ray-traversing surfaces(1 and e lie in part II.

In Fig. 3 each one of the parts I and 11 only contains one of these twosurfaces, i. e., part I the ray-entering surface d, and part I theray-exit surface e. The plane 7, as in Figs. 1 and 2, passes through thevertex A of said angle a, and the reflecting surfaces a and b, as inFig. 2, belon to part I, while the roof c belongs to part All of theprism-systems shown in Fig. 4 to Fi 7 correspond with Fig. 3 and differin dsu stance only by the size of angles a an B.

In Fig. 4 a=142 and ,B=8, while in Fig. 5 a=158 and ,8=22. In bothprism-systems the mutual distance 8 of the two raytraversing surfaces dand e is comparatively small.

In prism-systems Fig. 6 a=153 and B=13. The ray-entering surface d andthe ray-exit surface e lie in the plane f in which the parts I and IImeet each other. Of part I, piece ,Ia containing ineffective part b ofthe reflecting surface 6 is cut away.

In prism-system Fi 7, as in Fig. 6, a=153 and ,8=13. T e plane 7 isperpendicular to the two ray-traversing surfaces (1 and e. Theconstruction of part II is such that a part IIa protrudes at thickness1? beyond that surface a which embraces the angle a with the reflectingsurface 6.

I claim:

Reversing prism consisting of two parts cemented together and containingtwo raytraversing surfaces which are parallel to each other, a roofsurface and two nonsilvered single reflecting surfaces, the plane of oneof these two latter surfaces forming on the prism with the plane of oneof the said ray-traversin surfaces a. re-entering angle, the cementesurface passing through the line of intersection of the said two planes,and the said roof surface being the last reflecting surface struck by aray traversing the prism.

OTTO MOLLER.

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